It is a well known that poor lighting conditions can degrade the quality of digital images captured using digital image sensors. Small form factor cameras included in mobile or portable devices, such as those found in mobile phones and tablets, can exacerbate the issue. The race to shrink the form factor of mobile devices has led to smaller pixel sizes to reduce image sensor sizes, lower stack height of lenses (resulting in poor performing lenses), and smaller apertures to improve depth of field. While these changes have led to smaller camera modules, they have also led to poorer signal-to-noise ratio (SNR) as digital image sensors struggle to capture enough photons to produce signals stronger than the inherent noise within the camera system. As the lighting strength gets weaker this problem worsens exponentially.
While the digital imaging field struggles to deal with these issues through better sensor design and more robust algorithms, the simplest solution is to improve the incoming light signal to the image sensor. One method to improve the incoming reflected light signal is to increase the light level on the objects in the scene from which light is to be reflected and captured by the image sensor.
Mobile phones provide a small built in light source on the rear of the phone to accompany a rear camera for flash photography. However, these small built in light sources often have limitations in form factor and aesthetic design, as well as power and low cost requirements. As a result, these small built in light sources are typically very weak and often poorly designed for their intended purpose. These small built in light sources are usually utilized as a last resort, when no other lighting is provided around the mobile phone.
Smart phones and tablets often have a front camera that is used to capture a user's face for self portraits or video conferencing. Mobile device manufacturers assume that the user will use the front camera in well lighted conditions and thus do not provide a front built-in light source. The front camera is often smaller than the rear camera in a smart phone due to design limitations and aesthetics. Thus, without any front built-in light source, front facing cameras often do not capture images very well in dim or dark lighting conditions.